St. Charles's Seismic Design Category, explained

St. Charles carries Seismic Design Category B under USGS's ASCE 7-16 model. Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. Nationally, St. Charles ranks above 44% of the 4,875 cities in this dataset for seismic hazard - the 44th percentile.

How St. Charles compares

The raw figures: peak ground acceleration 0.069g, short-period spectral response 0.132g, 1-second spectral response 0.065g. Among 330 Illinois cities in this dataset, St. Charles ranks 100 for seismic hazard, the 70th percentile within the state. About 33,482 people live in St. Charles, Illinois.

What a retrofit costs in St. Charles

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for Illinois. A typical retrofit still runs $5,000-$10,000 nationally, about $7,000 for a common single-family job.

Insuring against this, not just retrofitting

Outside California, earthquake coverage is typically sold as an endorsement added to a standard homeowners policy, not a separate product - worth asking about directly when getting a home-insurance quote for a St. Charles address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced St. Charles's numbers. The guide to what a Seismic Design Category actually means covers why a category is never a substitute for an engineer's assessment of one specific house.